JRIV,
For what it's worth, we brief MSA why:
1) Situational awareness, in case of Emergency descent, or Engine Out Cruise or Loss of ATC when under vectors, the list goes on, comes under the general heading " Airmanship"
2) Ops manual specify max rate of descent within xx feet of MSA, for instance 3000 fpm within 3000 feet of the MSA, 2000, within 2000, 1000 within 1000 etc.
3) If we descend in VNAV, which is normal, with a tailwind or late descent cleared we may well be over the allowed ROD for the sector and rsik the hard warnings.
4) Even under radar vectors PM must state " below MSA" we have to know this for many reasons, windshear go-arounds, RA,s etc navigation with loss of FMS etc, ( this is not a clue for the raw data brigade to get on high horses)
In many parts of the world where there is a non-radar environment, Turkey for instance, you will not be cleared to a level below MSA until XXX DME and the controller know where you say you are. In this position the descent planning in the geometric path VNAV can be useless and again, " airmanship" comes into play.